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In the Forum: Melquiades Amplifier
In the Thread: A different breed of 6C33C amplifier.
Post Subject: Bias with attitude, bass and transformers...Posted by Romy the Cat on: 3/16/2012
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 KOTriode wrote:
Romy, in the contrary, it is very unfair to compare my 845 amp with the 6C33C. The main reason is the 845 amp used the best output/interstage transformer available, while the 6C33C's output xformer is pretty good but far from being best for the 6C33C. I can see sine wave distortion on the 6C33C at full power (15W) below 30Hz, while the 845 has no problem down to 20Hz (limit of my audio analyzer). Since there are not much 6C33C transformer availability out there, I just have to settle with what I have, but that's in the amplifier department.

Well, if you saw sine wave distortion at full power at 30Hz than whatever bass you heard from that amp was nothing to do with bass of 6C33C but it was just the inadequate quality of your output transformer. I hope you understand it.
 KOTriode wrote:
Now, the main reason that I built the 6C33C preamp is to experience the pure sound of 6C33C, with one cathode bias resistor/cap and a transformer load , it is as pure as it can be. It even have double output, one is through the output transformer, the second output using the transformer primary as choke load and output through a capacitor. It's output is pretty flat from 20Hz-20Khz with low distortion, sine wave looked pretty good at 20Hz, this is what I compared with a 845 preamp (even though with different output transformer), both do not have any other inoput/driver tube to inject their own sound. And it was these two preamp that lead me to compare the bass of the two tubes.

Yes. I do understand it but I have absolutely no experience with 6C33C in preamp. I know very well how 6C33C act as current buffer in power SET but I have no idea what the 6C33C needs at line level. It might have very different needed about wish I am not informed.
 KOTriode wrote:
When I described the 6C33C sound in the bass, I think you might have misunderstood that I criticized in a bad way. " On dynamic, the 6C33C tube showed its ability to go deep in the bass on Ray Brown trio recording of Soular Energy which is excellent for a 15W SE , the 845 amp can do better, but not by much, but probably because of its 25W output give it more headroom than the 6C33C"

Possibly it was your observation but it might be skewed by the specifics of your implementation. To have a common denominator for talking we need to talk about the publicly available 6C33C implementations. So, the only thing that I personally can testify is that I heard quite a few power amps with 845. I myself prefer amps around 211 as I feel it is softer sounding tube then 845 but it is not the point. The point is that any single power amp that I heard with 845/211 was absolutely no context in lower bass department to Lamm ML2.0. It is laughable how much ML2.0’s bass is better then pretty much any other SZET out there with 845/211 or pretty much with any other tube. The Lamm ML2.0 bass is better then any SS amp out there as well and in my view the Lamm ML2.0’s bass is the textbook bass as it has to be in audio, of cause if the amp has enough power to drive whatever it drives. That was my introduction to 6C33C bass and in my estimation the 6C33C still hold own, again, in my estimation.
 KOTriode wrote:
After living with 845 tubes over 20 years, with no less than 7 845 amplifier built, including 2 pair of push pull class a 50W and 100W(to satisfy my curiosity, I made a Parallel push pull with 4 845 tube per side to get 100w), I can say thay 845 is king in the bass area that no other tube can approach, now if the 6C33C being second best in the bass department at my first shot at it, I would say this tube is a miracle, I was so ecstatic adding this tubes to my stable and racing toward implementing it in a mono block version. I wish there are more output transformer available for the 6C33C, the Tango is too small to be serious, that leave Sowter and Lundahl, I might have left some others but if anybody know something I dont then I am all ears.

There are no good ready to go transformer for 6C33C. Tangos are garbage.  The 20 years back Tangos were OK for small tubes but Tango is long gone and whatever crap they label by Tango in fact Chinese transformers agglomerate production. Lundahl, with glass core, are very good in my view but they have small core size. At 200mA gap you will have 20Hz but if you build a full bloom 6C33C then you do not want to stop at 200mA. Your voltage is 200V, at 200mA you will have 40W on plate – way to little power, particularly for bass. I do not know the Sowter but generally I would advise to find somebody who would make for you your own custom transformer. Go for 350-400mA gap and for inductance to support 12-15Hz at 20W. There was a guy at my site who ordered one in Europe, I do not know if he like the results – he did not post any feedback. I guess you are American, so you might want o talk with somebody like David Slagle from NY. He is kind of “project guy” and he might be a good source for not cookie-cutter transformers with fast cores. Anyhow, the sound of nay SET is made at 85% by the sound of OPT. If you used any temp OPT to test your 6C33C then you get temp results and temp bass. I do not insist but I think that it is possible that as you get better and deserving OPT for your 6C33C then your view about the 6C33C bass will change.
 KOTriode wrote:
Regarding the Milq, it's not easy to modify my amp to the Milq cricuit, my amp was designed with DC coupled, therefore the B+ is pretty high, at about 500V it has twice the voltage of the Milq, the regulator cant regulate down to 220V without problem (too much voltage and current for the pass tube). To duplicate the Milq, it would  require different power transformer, but that can be done and I will put some thought into it.

I see, you use 6C33C as DC coupled with driver setting the bias – a dangers game for THIS tube. Anyhow, the idea of Milq is not the output tube but the driver tube and the way to bias the driver tube. Of your use the Milq’s driver tube with cathode bias or fixed bias then it will be very different sound that I very much do not endorse. Only with the bias as Milq has it the amp shows the sound that I like. Ironically, when I used the same Milq-style bias on the output tube then6C33C sounded like shit. The Milq driver and the way to bias THIS driver is very lucky combination in my view. BTW, if you use fixed bias on 6E5P and compare it with Milq bias then you will see that Milq bias show much much much more interesting bass…
Rgs, Romy the Cat

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